There is considerable interest in displays that provide a wide field-of-view, particularly in flight simulation and entertainment markets. Wide field-of-view displays overcome the inherent limitations of conventional cathode-ray tube (CRT) display technology, where display imaging is dimensionally and geometrically constrained to a generally flat, rectangular surface. Strategies for providing wide field-of-view displays have included tiling of projection surfaces, where multiple projectors each provide a portion of a tiled, panoramic image. Examples of tiled display systems using this type of approach to effect a wide field-of-view include the rear projection faceted dome disclosed in U.S. Pat. No. 5,179,440 issued Jan. 12, 1993 to Loban et al., and entitled “Rear Projection Facetted Dome” and dodecahedral imaging system disclosed in U.S. Pat. No. 5,023,725 issued Jun. 11, 1991 to McCutchen, and entitled “Method And Apparatus For Dodecahedral Imaging System.” Other types of systems provide a wide field-of-view by directing multiple projectors to a single curved screen, as is disclosed in U.S. Pat. No. 6,042,238 issued Mar. 28, 2000 to Blackham et al., and titled “Image Projection Display System For Use In Large Field-Of-View Presentation” and in U.S. Pat. No. 5,566,370 issued Oct. 15, 1996 to Young, and entitled “simulation Display System.”
As is well recognized, systems using multiple projectors are disadvantaged due to their high cost and due to the considerable effort needed for synchronization of multiple projected images. Among major disadvantages of tiled displays are differences between tiles, making it difficult to obtain uniform brightness, contrast, and color presentation from tile to tile. Related to this problem is the difficulty of eliminating or minimizing the visible display boundary between tiles. It is very difficult to effect a smooth transition between one tile and the next. In some applications, image uniformity across tile segments is very important, such as for collimated flight simulator displays, for example. In such applications, however, there can be significant ongoing cost and effort in order to maintain this tile-to-tile uniformity. For these reasons, conventional solutions for tiled wide field-of-view simulation systems have proved cumbersome and expensive, with disappointing image quality, low image brightness, and less than ideal image resolution.
As digital imaging technologies evolve, there is heightened interest in displays that provide a wide field-of-view, having sufficient brightness and high resolution. There are recognized advantages to displays that partially “surround” the viewer or operator with a panoramic view, taking advantage of a broader field of vision that could be provided. In addition to the demand in large-scale simulation and entertainment applications, wide field-of-view displays have also been considered for extending the usability of desktop computer workstation environments that currently use conventional windowing technology. For example, wide field-of-view displays are expected to find applications for improving CAD software operation, for improved control systems monitoring uses, and for numerous other types of applications. However, a number of obstacles currently prevent the widespread use of wide field-of-view displays, placing constraints on size, cost, image quality and resolution, and brightness.
Linear arrays, which can be considered as one-dimensional spatial light modulators, offer inherent imaging performance advantages, including the capability for high resolution, high brightness, low cost, and simple illumination optics requirements using laser sources. In many imaging applications, linear arrays are more suitable modulators for laser light than are their two-dimensional spatial light modulator counterparts, such as reflective and transmissive LCD and Digital Micromirror (DMD) devices. Grating Light Valve (GLV) linear arrays, as described in U.S. Pat. No. 5,311,360 issued May 10, 1994 to Bloom et al., and titled “Method And Apparatus For Modulating A Light Beam” are one earlier type of linear array that offers a workable solution for high-brightness imaging using laser sources, for example. Another experimental type of linear array just recently disclosed and in early development stages is the flexible micromirror linear array, as disclosed in U.S. patent application Ser. No. 2003/0048390 by Welch et al., published Mar. 13, 2003, and entitled “Video Projector And Optical Light Valve Therefor.” The prototype flexible micromirror linear array described in the U.S. patent application Ser. No. 2003/0048390 disclosure employs a line of reflective “microbridges” which are individually switched to modulate light to form a linear image.
Recently, an electromechanical conformal grating device consisting of ribbon elements suspended above a substrate by a periodic sequence of intermediate supports was disclosed by Kowarz in U.S. Pat. No. 6,307,663, entitled “Spatial Light Modulator With Conformal Grating Device” issued Oct. 23, 2001. The electromechanical conformal grating device is operated by electrostatic actuation, which causes the ribbon elements to conform around the support substructure, thereby producing a grating. The device of '663 has more recently become known as the conformal GEMS device, with GEMS standing for Grating ElectroMechanical System. The conformal GEMS device possesses a number of attractive features. It provides high-speed digital light modulation with high contrast and good efficiency. In addition, in a linear array of conformal GEMS devices, the active region is relatively large and the grating period is oriented perpendicular to the array direction. This orientation of the grating period causes diffracted light beams to separate in close proximity to the linear array and to remain spatially separated throughout most of an optical system. When used with laser sources, GEMS devices provide excellent brightness, speed, and contrast.
U.S. Pat. No. 6,411,425 issued Jun. 25, 2002 to Kowarz et al., and entitled “Electromechanical Grating Display System With Spatially Separated Light Beams” discloses an imaging system employing GEMS devices in a number of printing and display embodiments. As with its GLV counterpart or with a flexible micromirror linear array, a GEMS device modulates a single color and a single line of an image at a time.
Monocentric projection would clearly have advantages for providing an image on a surface having a generally cylindrical shape. However, for monocentric projection on a substantially cylindrical display screen, the ideal position for projection components is also the preferred viewer position. This problem, then, typically requires some type of off-axis solution. However, off-axis projection systems can be fairly complex and costly, particularly where a wide field-of-view is needed.
In spite of the shortcomings of prior art solutions, it is recognized that there would be significant advantages in providing an image display having a wide field-of-view. Freed from the “boxy” constraints of the conventional CRT model, a wide field-of-view display apparatus employing a curved display surface would be able to provide a more versatile and flexible environment, take advantage of additional display space, and provide a more enveloping visual environment suited to simulation, workstation, control monitoring, and entertainment applications.
Curved display surfaces can include both front and rear projection screens. Both front and rear projection screens can be directly viewed in some applications. In simulation environments, a curved display surface may not be directly viewed but may instead be used for providing an intermediate image to a curved mirror, as disclosed in U.S. Pat. No. 6,042,238 (Blackham et al.), for example. The curved mirror then provides a collimated virtual image of the intermediate image.
Thus, it can be seen that there is a need for an economical display apparatus providing a curved viewing surface having a very wide field-of-view, high resolution, good uniformity across the field, and high brightness.